1. Field of the Invention
This invention pertains to the art of reclosable plastic bags having extruded zippers, and more particularly to a reclosable bag having fastener profiles including wedge-shaped stops, which facilitate the joining attachment of the fastener profiles and which determine the amount of pull force required to open the bags. The fastener profiles are further of a design which makes inadvertent opening of the bags less likely.
The present invention also relates to reclosable plastic bags requiring a greater pull force to be opened from within than from without, and to a method for substantially reducing the variance in the forces required to open such bags from within and from without, as well as the consequent variability in the ratio between those forces.
The present invention further relates to a method for stabilizing and aligning the profiles of a plastic zipper during its attachment to a sheet of polymeric film, such as that used to make reclosable bags.
2. Description of the Prior Art
Reclosable bags used, for example, for storing household foodstuffs are typically made of polyethylene. As shown in U.S. Pat. No. 3,416,199 to Imamura commonly assigned with the present invention, a reclosable bag may be formed of two opposed walls equipped at the mouth with fastener profiles. These profiles include a male profile attached to one wall and a female profile on the other wall. The profiles are shaped so that, when they are aligned and pressed together into an engaging relationship, they form a continuous closure for the bag. The bag may be opened by pulling the walls apart thereby separating the profiles. Various geometric shapes and arrangements for such profiles are shown in U.S. Pat. Nos. Re. 28,969; 3,323,707; 4,212,337; 4,363,345; 4,561,108; and 4,812,056. In addition, U.S. Pat. Nos. 4,736,496 and 5,012,561 disclose reclosable bags with profiles and internal ribs adjacent to the profiles. U.S. Pat. No. 4,822,539 discloses a reclosable bag with interlocking profiles, internal guiding ribs disposed adjacent to the profiles, and stabilizing beams disposed on the outside surface of the bag wall. U.S. Pat. No. 3,338,285 discloses a reclosable bag having several parallel interlocking male and female profiles. In general, the profiles must be such as to provide relatively high resistance to opening from inside the bag while rendering the bag relatively easy to open from the outside.
For the zipper to function properly, it is important that the zipper components (i.e. the profiles and any wedges, beams, ribs or the like provided to enhance the operation of the profiles) maintain their alignment. The problem of maintaining the alignment of the components of the zipper is exacerbated where the zipper is in string or strip form to be heat sealed to a film material from which the body of the bag is to be formed, since the heat necessary to fuse the zipper strip to the film could distort the profiles or a zipper component. Heretofore, the problem has been avoided by adding webs to the zipper strip to separate the profiles (and components) from the point of attachment to the film. In U.S. Pat. No. 4,673,383 a zipper strip is disclosed having fusible ribs on its undersurface to minimize the heat to which the zipper is subjected. In U.S. Pat. Nos. 4,691,372; 4,731,911; and 4,817,188, an adhesive layer is provided on the base of the profile portion of the strip.
Another aspect of the problem of maintaining the alignment of the components during heat-sealing to a film material is reflected in the ability of the profiles to rock relative to one another about a longitudinal axis because a male interlocking member may pivot within a female interlocking member about such an axis. This ability to rock or pivot presents an instability of the two profiles relative to one another which may have an adverse effect on the quality of the heat-seal between the profiles and the film material.